On Thursday, Foreign Secretary William Hague called on other ministers and leading figures in Tripoli to follow Koussa’s example.

“We encourage those around Gaddafi to abandon him and embrace the better future for Libya that allows political transition and real reform and meets the aspirations of the Libyan people,” said the Foreign Secretary.

We encourage those around Gaddafi to abandon him and embrace the better future for Libya. William Hague

“Moussa Koussa is one of the most senior members of the Gaddafi regime and has been my channel of communication to the regime in recent weeks and I have spoken to him several times on the telephone, most recently last Friday (25 March).”

Reporting from Tripoli, our Foreign Affairs correspondent Jonathan Rugman says that, given this recent contact, it may yet transpire that Moussa Koussa’s value as a defector is possibly less than his value as a negotiator within the Gaddafi regime.

However, persuading those in Gaddafi’s clique to abandon him will not be as straighforward as getting in a car and heading for the Tunisian border. A defector from the regime, who now lives in Europe, has told Channel 4 News that Gaddafi “detains family members” of those close to him.

Reports are emerging that Koussa was accompanied in his journey to Tunisia earlier this week by a cavalcade of cars, the suggestion being that he was accompanied by his family.

"Moussa Koussa was actually named within our legal actions within the USA due to his alleged unprecedented involvement within the IRA that killed and maimed countless UK and Irish citizens," says Jonathan Ganesh, a survivor of the Docklands bomb attack and spokesman for IRA victims.

"He is unprecedented senior member of the regime that was involved in crimes against humanity which caused unimaginable suffering to countless innocent people within the UK.

"I personally was astonished that the UK Government received this man last night but I was pleased to be informed today that he will not be granted immunity from prosecution and actions that may take place within ICC.

"We feel that it is very important that no member of this evil Libyan regime, who it can be established committed crimes against humanity, is exempt from the law.

"I have received numerous calls from IRA victims and their families today who have advised that they hold Mr Koussa equally responsible for the loss of their member of their family due to his alleged involvement with the IRA.

"I feel that the intelligence that this man could provide to the UK concerning unsolved matters such as the WPC Fletcher's murder, Lockerbie and the support extended to the IRA during their murderous campaign could finally bring closure to these countless families.

"I also feel his defection from the regime may actually encourage other to defect from this evil dictator.

"Gaddifi and his evil regime must be held to account due to the murder of countless innocent people within the UK and around the world."

‘Other key figures will defect’

A friend of Mr Koussa’s, Noman Benotman – a senior analyst at Quillium, told Channel 4 News this was “devastating” for Gaddafi’s regime: “He is a key figure and is a heavyweight. This is a huge upset for the Libyan Government.”

Mr Benotman said he was sure Mr Koussa had influenced other key figures in the Libyan regime and there would be more defections.

He also warned the world would be watching how Mr Koussa was treated by Britain: “I think he will cooperate with the British Government. He trusts the British values and systems.

“This was a very bold move. He decided he can’t end his career as a Libyan politician. He can’t be participating in murder against his own people.”

However, Channel 4 News Foreign Affairs Correspondent, Jonathan Rugman, suggests that Koussa’s productive relationship with Britain in recent years could make him believe he can successfully seek asylum. He also says that Gaddafi’s propaganda machine has moved into gear as the regime seeks to renounce Koussa and downplay his former role.

Tipping point? "In his role as Gaddafi's intelligence chief in the 1980s and 1990s, Koussa is suspected by some of being the mastermind of the Lockerbie bombing. He was also involved in the negotiations surrounding the release of the only man ever convicted for the terrorist attack, Abdelbaset el-Megrahi, writes Channel 4 News Foreign Affairs Correspondent Jonathan Rugman.

"A Libyan spokesman said Koussa had not defected and was travelling on a diplomatic mission. Koussa, Western-educated and English speaking, was the architect of a dramatic shift in Libya's foreign policy that brought the oil-producing desert stateback to the international community after years of sanctions. A potential benefit to the West from his defection is that if he decides to share his knowledge he could reveal valuable information about how the Gaddafi administration functions and the weak points that could be exploited to bring Gaddafi down.

"British officials were also keen to establish what role, if any, Koussa wished to play in the anti-Gaddafi coalition. Some of other ministers and ambassadors who have resigned since the revolt started in February have joined the opposition."We encourage those around Gaddafi to abandon him and embrace a better future for Libya that allows political transition and real reform that meets the aspirations of the Libyan people," Britain's Foreign Office said. However, despite Koussa's influential position, Gaddafi's innermost circle is made up principally of his sons and people with family ties, and their loyalty is likely to be more robust. Earlier this month, U.S. Secretary of State Hillary Clinton said she was aware that people close to Gaddafi had been trying to make contact. British Foreign Secretary William Hague has kept in contact with Koussa during the mounting crisis in Libya."

Challenged"In the course of my interview, I challenged the Deputy with this information. Even though we were connected by little more than a jumped-up video phone, his face – two foot high in the studio wall in front of me – was clear. I saw in that very moment, a flicker, a flicker I could well have missed had we been face to face.

"The flicker, together with a miniscule pause and change in the timbre of his voice told me I had hit home.

'He has been in Tunisia, he is back, he is in a meeting later tonight,' the Deputy told me. Oh yes? Our informant had talked of Koussa having travelled to Tunisia in a road convoy…if he really were back, it would have to have been by plane, at night, under bombardment from the enforcement of the no-fly zone. I rapidly concluded, Moussa Koussa: no fly. Moussa Koussa had defected!"

In his role as Gaddafi’s intelligence chief in the 1980s and 1990s, Koussa is suspected by some of being the mastermind of the Lockerbie bombing.

He was also involved in the negotiations surrounding the release of the only man ever convicted for the terrorist attack, Abdelbaset el-Megrahi.

A potential benefit to the west from his defection is that if he decides to share his knowledge he could reveal valuable information about how the Gaddafi administration functions and the weak points that could be exploited to bring Gaddafi down.

British officials were also keen to establish what role, if any, Koussa wished to play in the anti-Gaddafi coalition. Some of other ministers and ambassadors who have resigned since the revolt started in February have joined the opposition.

Familes of Lockerbie bombing rejoice

The father of a victim of the Lockerbie bombing said he is “delighted” that Koussa is in the UK, because he hope that he will be given the opportunity to speak to the former Foreign Minister with a view to shedding greater light on the atrocity.

Dr Jim Swire’s daughter Flora was among the 270 killed when Pan Am Flight 103 exploded on 21 December, 1988, and he has been the main English organiser of British victim support.

“I’m over the moon because this guy knows everything about the efforts of the Gaddafi regime over the past 30-40 years,” he said. “So he was right at the centre of things in Libya at the time that Lockerbie happened.”

Dr Swire met Koussa in 1991 and described the encounter as “more terrifying than meeting Gaddafi”.

I’m over the moon because this guy knows everything about the efforts of the Gaddafi regime. Dr Jim Swire, whose daughter Flora died in the Lockerbie bombing

“I first met him to ask Gaddafi to ask his citizens to appear in front of the Scottish court. I found the interview with Moussa Koussa pretty terrifying. Throughout the hour or so of the interview there were minions coming and going and iy was obvious that he was dispersing power around the country. It was a very scary time, far more scary than meeting Col Gaddafi, actually.”

But he warned that any information volunteered by Koussa should be scrutinised intently. He said: “We have to remember that whatever he says, he’ll be saying in a situation where he’ll be trying to save his own skin because he’s reneged on Gaddafi and thrown himself on the mercy of the West; and so what he will say, no doubt will be likely to blacken the regime he’s just left and I think anything he says should be taken with great caution.”

Dr Swire added that he has spoken with his lawyers and hopes to be able to get another opportunity to talk to him .

A Libyan spokesman said Koussa had not defected and was travelling on a diplomatic mission.